Fagnant-Sperati, C.S.Ren, Y.Zhou, N.A.Komen, E.Mwangi, B.Hassan, J.Chepkurui, A.Nzunza, R.Nyangao, J.Van Zyl, Walda B.Wolfaardt, MarianneMatsapola, P.N. (Peter)Ngwana, F.B. (Fhatuwani)Jeffries-Miles, S.Coulliette-Salmond, A.Pe~naranda, S.Vega, E.Shirai, J.H.Kossik, A.L.Beck, N.K.Boyle, D.S.Burns, C.C.Taylor, M.B.Borus, P.Meschke, J.S.2020-11-042020-11-042021-03Fagnant-Sperati, C.S., Ren, Y., Zhou, N.A. et al. 2021, 'Validation of the bag-mediated filtration system for environmental surveillance of poliovirus in Nairobi, Kenya', Journal of Applied Microbiology, vol. 130, no. 3, pp. 971-981.1364-5072 (print)1365-2672 (online)10.1111/jam.14807http://hdl.handle.net/2263/76699SUPPORTING INFORMATION: Appendix S1. Nairobi environmental surveillance sites. Appendix S2. Statistical methods. Appendix S3. Replicate BMFS samples. Appendix S4. Samples included in statistical analyses. Appendix S5. NPEV detection in BMFS and two‐phase samples.AIMS : This study compared the bag-mediated filtration system (BMFS) and standard WHO two-phase separation methods for poliovirus (PV) environmental surveillance, examined factors impacting PV detection and monitored Sabin-like (SL) PV type 2 presence with withdrawal of oral polio vaccine type 2 (OPV2) in April 2016. METHODS AND RESULTS : Environmental samples were collected in Nairobi, Kenya (Sept 2015–Feb 2017), concentrated via BMFS and two-phase separation methods, then assayed using the WHO PV isolation algorithm and intratypic differentiation diagnostic screening kit. SL1, SL2 and SL3 were detected at higher rates in BMFS than two-phase samples (P < 0 05). In BMFS samples, SL PV detection did not significantly differ with volume filtered, filtration time or filter shipment time (P > 0 05), while SL3 was detected less frequently with higher shipment temperatures (P = 0 027). SL2 was detected more frequently before OPV2 withdrawal in BMFS and two-phase samples (P < 1 9 10 5). CONCLUSIONS : Poliovirus was detected at higher rates with the BMFS, a method that includes a secondary concentration step, than using the standard WHO two-phase method. SL2 disappearance from the environment was commensurate with OPV2 withdrawal. SIGNIFICANCE AND IMPACT OF THE STUDY : The BMFS offers comparable or improved PV detection under the conditions in this study, relative to the twophase method.en© 2020 The Authors. Journal of Applied Microbiology published by John Wiley & Sons Ltd on behalf of Society for Applied Microbiology. This is an open access article under the terms of the Creative Commons Attribution License.Enteric virusesEnvironmental surveillanceFiltrationKenyaPoliovirusViroCapWastewaterBag-mediated filtration system (BMFS)Standard WHO two‐phase separation methodsArticle